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#1
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3/8" Fuel System-how much power?
I have read a number of articles on fuel systems, and am trying to get a better feel as to when upgrades are needed (as opposed to waiting until symptoms appear).
In my case, I have a 3/8" factory style pickup with 3/8" steel line running to a factory style pump (with return) and 3/8 steel line to a qjet. This setup has worked fine on a 420hp 455. But as always, performance upgrades trickle in here and there to make more power... As a general rule, how much power should this setup support? 450? 500hp? When is a good rule to start moving to a 1/2" system? It would be good to hear what some of your experiences have been! Thanks. |
#2
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On the dragstrip (not so much on the street) I started having issues at 400 hp with the stock lines and carter mechanical. Went to 1/2 pickup and lines. Didnt fix problem... sumped tank and electric pusher fixed it. So you are already doing better than i did with stock lines and mechanical pump. Fwiw
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs ([_|_] ##\|/##[_|_]) |
#3
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You are probably aware of this but the dual quad 421 super dutys ran 3/8" lines back in the day.
I know nothing about quadrajets but for AFBs and Rochester 2bbls I've found that the seats under the needles in current manufacture sets are not large enough to allow the fuel pump to keep up with the engine on tripowers or dual quads when people want to go 1/4 mile drag racing; so I drill them out larger. That is the first thing I tell people to check when they start running out of gas part way down the track. But we're talking nostalgia type 400-600hp engines here and not all out modern racing engines. |
#4
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I have a tri-power on my 440 that seems to run out of fuel near 5600 rpm, even though I have a Robbmc 550 mech pump and 1/2" tank pickup, along with 1/2 aluminum line from tank to pump. Thinking of going with a sumped tank with an electric pusher, that only comes on at WOT via a micro switch mounted at carb. But if the carb inlets are such a restriction, this might not make much of a difference
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66 GTO, 495, M22, Strange S-60 w/4.10 Sold new at Ace Wilson's Royal Pontiac http://www.youtube.com/watch?v=cUHC-Z8xhtg |
#5
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The Rochester carb needles and seats have a inlet inside diameter of .117" (The typical Holley Double Pumper has a .110" needle and seat in each Bowl. The HIGH PERF needles and seats are .120"). So you have a Tri Power with THREE .117" needles and seats (FIFTY PERCENT MORE FUEL AVAILABLE) vs a typical Holley High Performance 4-BBL carb. I believe you have other issues, personally. Years ago I had a TRI POWER set-up fed by both a mechanical fuel pump and a Holley Blue (noisy sucker) electric fuel pump. The fuel circuit had a by-pass circuit where the mechanical fuel pump could draw fuel from the tank without it having to pass through impeller vanes of the Holley Pump when th3e electric pump was off. The circuit also had a check valve that closed when the electric pump was on. This kept the electric pump from just sending fuel right back to the tank vs forward to the mechanical pump. The pump was triggered by a on-off switch but today I would use a NOS trigger switch and turn on a high amp relay that supplied 30 amp current to the electric fuel pump. A Holley Blue Pump would be my LAST choice for the pump. Other Modern Holley Pumps or the Carter pumps should work fine. Tom Vaught ps My fuel pick-up was extended and was closer to the rear of the tank vs in the stock location. More like 3/4 to the rear.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
The Following User Says Thank You to Tom Vaught For This Useful Post: | ||
#6
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But I don't want to hurt performance when the electric pump is not running, and a check valve in the bypass line would be an additional restriction. I've thought that a solenoid valve might be better since there would not be much of a pressure drop through it when pulling just with the mechanical pump. Or maybe enough fuel would also flow through the vanes so the check valve restriction is not an issue. Any thoughts?
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1969 Lemans vert, matador red, 462 CI, 3.07 12-bolt posi 1974 455 TA, admiralty blue/red interior HPP "cover car" - sold "The best way to show a car is to drive it" |
#7
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I don't believe a check valve would restrict flow during normal driving. And having a throttle mounted switch that was only on during wot, you probably wouldn't hear the electric pump over the exhaust. And with this setup, the electric pump would only be on for a few seconds anyway
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66 GTO, 495, M22, Strange S-60 w/4.10 Sold new at Ace Wilson's Royal Pontiac http://www.youtube.com/watch?v=cUHC-Z8xhtg |
#8
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#9
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I feel it should rev past 6000 easily with the 252/262 @ .050 sft cam that I have.
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66 GTO, 495, M22, Strange S-60 w/4.10 Sold new at Ace Wilson's Royal Pontiac http://www.youtube.com/watch?v=cUHC-Z8xhtg |
#10
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#11
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#12
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I run a 255 LPH in-tank fuel pump designed for a FI vehicle with a RobbMC return style regulator feeding Tri-Power Carbs. The regulator does just fine at reducing the pressure from 60+ PSI to 5 PSI or less. I have 1/2" lines to and from the regulator. I have been running this setup for over 5 years without any apparent issues.
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The Following 2 Users Say Thank You to Joel Koontz For This Useful Post: | ||
#13
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I had/have a fuel pressure guage i can see while driving. On WOT runs i could watch the pressure go down to <1lb. Then caput... were the super duty tanks baffled or sumped? The dual quad setups would have provided a much larger reserve than a single Qjet.
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs ([_|_] ##\|/##[_|_]) |
#14
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Dual quad 409s also had a 3/8 line. With my old low 12s 109 mph car I added a Carter electirc just because back then. Sucked that $0.30/gallon leaded down pretty fast!
My TA's fuel history-factory pump factory lines good for stock motor. Stock rebuild but added a bigger cam 228/228 -ran out of fuel top of second. Wired and eltric fuel pressure gauge and watched it drop.Tried different mechanicals Holley /Carter helped a little but needed a helper mini AC Delco electric. We are talking a mild low compression 400 in the 14a Then added the 420hp 455 with the Qjet- not as bad but had to jump to a 140 Mallory to the Holley mechanical. Open headers-nope had to go 1/2 from the pump to the Qjet and dropped the mechanical. Still have the 3/8 pickup no sock in the tank and it is supporting 550+ HP no problems.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#15
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Worthy debate. i favor using 3/8" steel lines into the 11's. Seems the total suite of Bend methods, pickup, pusher pump, mechump & carb Seat(s) orifice, & float setting(s) will call successful folks into question by the many that fuel-starve.
my 12.0 car has 3/8" steel lines. My 12.2 car has not yet repeated such perf & it may be the fueldelivery leaning out. Or maybe the next run will be 11's. I dunno. yet, 1/2" aluminum fuel line seems affordable & installs real nice with flare fittings. clamps help with reliability.
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12.24/111.6MPH/1.76 60'/28"/3.54:1/SP-TH400/469 R96A/236-244-112LC/1050&TorkerI//3850Lbs//15MPG/89oct Sold 2003: 12.00/112MPH/1.61 60'/26"x3.31:1/10"/469 #48/245-255-110LSA/Q-Jet-Torker/3650Lbs//18MPG 94oct Sold 1994: 11.00/123MPH/1.50 60'/29.5"x4.10:1/10"/469 #48/245-255-110LSA/Dual600s-Wenzler/3250Lbs//94oct |
#16
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If someone is starting fresh on a fuel system, i dont know why anyone would do a 3/8" line and a stock sender unless its a correct resto. The only time this should even be a debate is if everything is already in place but then my answer would be to just run it and see. You already have everything in place. See what happens. If you dont want any problems then upgrade to 1/2" line and a good fuel pump. RobbMc makes good extended tube sending units and Tanks inc. Makes a lot of tanks setup for walbro pumps with correct baffleing.
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-1967 GTO HO Restomod. PKMM 433ci, SilverSport T56 Magnum 6spd, Moser 9", SC&C and a bunch of other pro touring goodies - Build Thread http://forums.maxperformanceinc.com/...615847&page=23 Last edited by Nicks67GTO; 02-08-2014 at 12:58 AM. |
#17
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I ran 114mph with a 3/8 line but with a half inch pickup and a Mallory 140 pump.Replaced the 3/8 line with all 8AN and picked up a solid 2mph plus.My current with a few combo changes runs 118 plus....but...the pressure still drops to 3.5 lbs at 1000ft...Next step is sumping the tank and moving the pump.
One of the best investments in any higher hp car is a fuel pressure gauge that you can see. |
#18
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My Trans Am ran 12.09 @ 113 With the 3/8 lines and a Stock fuel pump.
The sock was removed from the pick up. My GTO ran 11.79 @ 116 with the 3/8 lines and a Holley mechanical pump. |
#19
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Drag racing with good traction will require a LOT more attention to fuel delivery than street driving.
I never had any issues anyplace on the street with my old 428 engine, Continental converter and 3.42 gears. It was fed by stock pick-up, stock lines, and Carter HP mechanical pump. At the track it would nose over right at the top of first gear every single run. That problem was solved by putting a Holley red pump in front of the tank. That set-up was good to high 12's, then fuel delivery issues cam back when I installed my first 455 engine making 455hp. I got around that deal by bypassing the mechanical pump. The car ran mid 12's for several years, but I always thought it felt a tad "soft" up near the shift point. Everyone kept saying to put a Holley on the engine because the fuel bowl in the q-jet was too small, so I did, and it ran no faster anyplace. I went ahead and drove and raced the car for a couple more years, most runs between 12.40 to 12.60 at 108-109MPH, best ever 12.37 at 109MPH. Over one Winter I sumped the tank, installed a Comp 140 pump behind the tank, and 8an lines/fittings everywhere. The very first runs the next season were 12.0's at 112MPH, no other changes! I even put the big 850 Holley back in place and it ran about the same ET and MPH as the Q-jet. A few months later we were asked to do the KRE dyno/track testing, and the car went down to 11.70's at 114-115mph. I went on to install a 455 with even more power, and the car has went 11.30's over 120mph without the first hint of fuel delivery issues anyplace. This topic gets kicked around quite a bit, and I've seen a few folks post running really quick with stock fuel delivery systems, where most folks can't get out of the 13's trying to do the same thing. The size/shape of the tank plays a role here, as with most it's pretty easy to uncover the pick-up in the tank on hard launches. I would also suppose that how the fuel line is routed, subjected to any heat, and how many bends are in it play a role as well. Of course fuel pump location, and flow rate jump in there too, and how free flowing the filter(s) are would also impact the results. I would also imagine that even when we see pretty good results with stock parts, that those folks still may not be running as quick as they could with better parts. As I found out with my own car, it ran clear down to 12.37 at 109 and pulled right up to the shift point of 5500rpm's. However, when I upgraded the fuel system, the engine pulled noticeably harder at high rpms, and the tach whizzed past 5500rpm's so fast I actually over-revved the engine on the first two track runs......Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
The Following User Says Thank You to Cliff R For This Useful Post: | ||
#20
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This is interesting. I always assumed fuel delivery issues would be obvious in a carb engine with stumbling, missing, etc. Thank you all for the great info!
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